It is proposed to relate the depression in the content of cytoplasmic poly (A)-containing RNA to the inhibition of increased turnover of small molecular weight nuclear non-histone proteins. The sequence in which these effects are manifested should indicate whether the inhibition of poly (A) synthesis by aminonucleoside results in a depression in the turnover of nuclear proteins, or vice versa. The effect of aminonucleoside on the synthesis of heterogenous nuclear RNA in normal and transformed cells will be studied, as well as its effect on poly-adenylation of that RNA in the nucleus. Effect of aminonucleoside on polysome integrity and on the synthesis of other species of RNA will be studied by sucrose gradient centrifugation of isotopically labeled RNA, in order to determine the specificity of inhibition of poly (A)-containing RNA by aminonucleoside.